The art of printing images with micro-fluid technology is relatively well known. A permanent or semi-permanent ejection head has access to a local or remote supply of fluid. The fluid ejects from an ejection zone to a print media in a pattern of pixels corresponding to images being printed.
Micro-fluid ejection heads, also known as printheads, may be classified in several categories which include thermal inkjet printheads or piezoelectric inkjet printheads. Thermal inkjet printheads use resistive heating elements to heat liquid ink to form vapor bubbles which force ink droplets onto a media through a nozzle. Thermal inkjet printheads typically use aqueous ink, which is a mixture of water, glycol and pigments (or dyes). Superheated water in aqueous ink favorably provides thermal inkjet printheads with a high initial pressure of about 100 atm. Piezoelectric inkjet printheads, on the other hand, use piezoelectric actuators to form pressure pulses which force ink through a nozzle hole onto a media. Unlike thermal inkjet printheads, piezoelectric inkjet printheads allow the use of a wider range of inks including solvent based inks and UV curable inks. In addition, piezoelectric printheads are advantageous in various applications that require use of heat-sensitive fluids such as in biological and medical printing or dispensing applications. However, piezoelectric printheads are known to be more expensive and more difficult to fabricate compared to thermal inkjet printheads.
Piezoelectric printheads are typically fabricated by complex processes to form pressurizing chambers and fluidic structures. A piezoelectric printhead constructed by stacking and binding several layers together is disclosed, for example, in U.S. Pat. No. 7,611,231. In some practices, piezoelectric actuators are manufactured using a ceramic processing and later combined with the fluidic structures by assembly processes as disclosed, for example, in U.S. Pat. Nos. 5,956,829 and 5,548,314. In one particular application, piezoelectric actuators are fabricated by laminating alternative layers of piezoelectric layers and electrode layers and sintering the layers together. The sintered plate is divided into individual actuator fingers by dicing. The result, however, are actuators that are fragile which need careful handling when assembled with fluidic structures.
U.S. Pat. No. 6,629,756 describes piezoelectric printheads using a thin film piezoelectric layer instead of bulk piezoelectric ceramics or screen printed piezoelectric layers. Usage of a thin film piezoelectric layer eliminates complex processes described previously. However, forming pressure chambers by a deep reactive ion etching (DRIE) and attaching pre-formed fluidic structures by a bonding process is still required. Although DRIE enables manufacturers to define pressure chambers more accurately than anisotropic silicon wet chemical etching, it is still challenging to create fine pitched and high aspect ratio pressurizing chambers from the back side of a substrate by etching its full thickness. For example, a 360 dpi printhead with a 70.6 um spacing between adjacent nozzles and 50 um wide pressure chamber would only have a 20.6 um wall thickness between two adjacent pressure chambers. Without controlling the chamber wall angle accurately during DRIE, it is challenging to define pressure chambers uniformly on a large wafer. In addition, the process requires an accurate front to backside alignment. These kinds of complex manufacturing processes reduce production yield and increase manufacturing cost of piezoelectric printheads.
Accordingly, a need exists in the art to eliminate complex process steps required to fabricate piezoelectric printheads and prevent piezoelectric printheads from being batch-processed in wafer level. Additional benefits and alternatives are also sought when devising solutions.